Synchronization of multiple mmwave devices

ABSTRACT

In an embodiment, a method includes: receiving a global trigger with a first millimeter-wave radar; receiving the global trigger with a second millimeter-wave radar; generating a first internal trigger of the first millimeter-wave radar after a first offset duration from the global trigger; generating a second internal trigger of the second millimeter-wave radar after a second offset duration from the global trigger; start transmitting first millimeter-wave radar signals with the first millimeter-wave radar based on the first internal trigger; and start transmitting second millimeter-wave radar signals with the second millimeter-wave radar based on the second internal trigger, where the second offset duration is different from the first offset duration, and where the first and second millimeter-wave radar signals are transmitted sequentially so as to exhibit no temporal overlap.

This application claims is a continuation application of U.S. patent Ser. No. 16/779,104, filed on Jan. 31, 2021, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to an electronic system and method, and, in particular embodiments, to synchronization of multiple millimeter-wave (mmWave) devices.

BACKGROUND

Applications in the millimeter-wave frequency regime have gained significant interest in the past few years due to the rapid advancement in low cost semiconductor technologies, such as silicon germanium (SiGe) and fine geometry complementary metal-oxide semiconductor (CMOS) processes. Availability of high-speed bipolar and metal-oxide semiconductor (MOS) transistors has led to a growing demand for integrated circuits for millimeter-wave applications at 24 GHz, 60 GHz, 77 GHz, and 80 GHz and also beyond 100 GHz. Such applications include, for example, automotive radar systems and multi-gigabit communication systems.

In some radar systems, the distance between the radar and a target is determined by transmitting a frequency modulated signal, receiving a reflection of the frequency modulated signal (also referred to as the echo), and determining a distance based on a time delay, phase, and/or frequency difference between the transmission and reception of the frequency modulated signal. Accordingly, some radar systems include a transmit antenna to transmit the radio-frequency (RF) signal, a receive antenna to receive the RF, as well as the associated RF circuits used to generate the transmitted signal and to receive the RF signal. In some cases, multiple antennas may be used to implement directional beams using phased array techniques. A multiple-input and multiple-output (MIMO) configuration with multiple chipsets can be used to perform coherent and non-coherent signal processing as well.

SUMMARY

In accordance with an embodiment, a method includes: receiving a global trigger with a first millimeter-wave radar; receiving the global trigger with a second millimeter-wave radar; generating a first internal trigger of the first millimeter-wave radar after a first offset duration from the global trigger; generating a second internal trigger of the second millimeter-wave radar after a second offset duration from the global trigger; start transmitting first millimeter-wave radar signals with the first millimeter-wave radar based on the first internal trigger; and start transmitting second millimeter-wave radar signals with the second millimeter-wave radar based on the second internal trigger, where the second offset duration is different from the first offset duration, and where the first and second millimeter-wave radar signals are transmitted sequentially so as to exhibit no temporal overlap.

In accordance with an embodiment, a system includes an application processor, and first and second millimeter-wave radars. The application processor is configured to generate a global trigger. The first millimeter-wave radar includes: a first timer configured to generate a first internal trigger after a first offset duration from the global trigger, a first millimeter-wave radar sensor circuit, and a first controller configured to generate first millimeter-wave radar signals based on the first internal trigger using the first millimeter-wave radar sensor circuit. The second millimeter-wave radar includes: a second timer configured to generate a second internal trigger after a second offset duration from the global trigger, a second millimeter-wave radar sensor circuit, and a second controller configured to generate second millimeter-wave radar signals based on the second internal trigger using the second millimeter-wave radar sensor circuit, where the second offset duration is different from the first offset duration so that the first and second millimeter-wave radar signals are transmitted sequential and without temporal overlap.

In accordance with an embodiment, a system includes an application processor, and first and second millimeter-wave radars. The application processor is configured to generate a global trigger. The first millimeter-wave radar includes: a first trigger terminal configured to receive the global trigger, a first timer configured to generate a first internal trigger after a first offset duration from the global trigger, a first millimeter-wave radar sensor circuit, and a first controller configured to generate first millimeter-wave radar signals based on the first internal trigger using the first millimeter-wave radar sensor circuit. The second millimeter-wave radar includes: a second trigger terminal configured to receive the global trigger, a second timer configured to generate a second internal trigger after a second offset duration from the global trigger, a second millimeter-wave radar sensor circuit, and a second controller configured to generate second millimeter-wave radar signals based on the second internal trigger using the second millimeter-wave radar sensor circuit, where the second offset duration is different from the first offset duration so that the first and second millimeter-wave radar signals are transmitted sequentially and without temporal overlap.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a flow chart of an embodiment method for synchronizing multiple millimeter-wave radars, according to an embodiment of the present invention;

FIG. 2 shows waveforms of signals of a millimeter-wave radar system, according to an embodiment of the present invention;

FIG. 3 illustrates chirp transmissions and power amplifier states of the millimeter-wave radars of FIG. 2 , according to an embodiment of the present invention;

FIG. 4 shows a flow chart of an embodiment method for programming and synchronizing multiple millimeter-wave radars, according to an embodiment of the present invention; and

FIGS. 5 and 6 show schematic diagrams of millimeter-wave systems, according to embodiments of the present invention.

Corresponding numerals and symbols in different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments disclosed are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

The description below illustrates the various specific details to provide an in-depth understanding of several example embodiments according to the description. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials and the like. In other cases, known structures, materials or operations are not shown or described in detail so as not to obscure the different aspects of the embodiments. References to “an embodiment” in this description indicate that a particular configuration, structure or feature described in relation to the embodiment is included in at least one embodiment. Consequently, phrases such as “in one embodiment” that may appear at different points of the present description do not necessarily refer exactly to the same embodiment. Furthermore, specific formations, structures or features may be combined in any appropriate manner in one or more embodiments.

Embodiments of the present invention will be described in a specific context, a circuit and method for synchronization of multiple millimeter-wave devices, such as millimeter-wave radars. Embodiments of the present invention may be used to synchronize other types of millimeter-wave devices, such as 5G communication devices, e.g., operating in multiple-input multiple-output (MIMO) configuration. Some embodiments may be used to synchronize other types of devices that do not operate in the millimeter-wave frequency regime.

In an embodiment of the present invention, multiple devices are synchronized by using a local synchronization circuit implemented in each of the multiple devices. A global trigger is sent to each of the multiple devices instead of using dedicated triggers for each device. Timing in each device is based on the local synchronization circuit and the global trigger.

In many applications, multiple devices rely on a synchronization mechanism during normal operation. For example, in some applications, multiple millimeter-wave radars that are located in different portions of a printed circuit board (PCB) rely on a synchronization mechanism, e.g., to avoid radio-frequency (RF) interference of transmitted chirps and/or to perform functions such as beamforming. Conventionally, an application processor synchronizes the millimeter-wave radars by sending dedicated trigger signals, at appropriate times, to each of the millimeter-wave radars using dedicated lines electrically connected to each of the millimeter-wave radars. In other words, the burden is placed on the application processor to ensure correct timing.

In an embodiment of the present invention, a local synchronization circuit implemented in each millimeter-wave radar is used to control the timing of chirps based on a common global trigger. Each local synchronization circuit has a unique time offset that delays the start of the first chirp by a unique offset duration. In some embodiments, an identical finite state machine (FSM) is used in each radar to control the timing between chirps, the duration of each chirp, and the start of the first chirp, where the delay applied by each finite state machine is, e.g., programmed to be unique to each millimeter-wave radar.

FIG. 1 shows a flow chart of embodiment method 100 for synchronizing multiple millimeter-wave radars, according to an embodiment of the present invention.

During step 102, a global trigger is sent, e.g., by an application processor, to a set of millimeter-wave radars. In some embodiments, the global trigger is sent using a trigger line, e.g., a PCB trace, connected to a general purpose I/O (GPIO) terminal of the application processor, where the trigger line is connected to a trigger terminal of each of the millimeter-wave radars. In some embodiments, the global trigger is sent using a communication interface, such as inter-integrated circuit (I²C) or serial peripheral interphase (SPI). For example, in some embodiments, the global trigger may be sent using SPI Broadcast Mode, such as described in co-pending U.S. patent application Ser. No. 16/779,126, filed on the same day as this application, entitled “SPI Broadcast Mode,” and associated with Attorney Docket No. INF 2019 P 56018 US, which application is hereby incorporated herein by reference.

During step 104, each of the millimeter-wave radars receive the global trigger and starts a respective local timer based on the global trigger. In some embodiments, the local timer is implemented with a digital counter. For example, in some embodiments each local counter counts up to a predetermined count, where the predetermined count is different for each of the millimeter-wave radars of the set. In some embodiments, each predetermined count may be programmed, e.g., using SPI, e.g., by the application processor.

During step 106, when the respective local timer expires (e.g., when the digital counter reaches the predetermined count), the respective millimeter-wave radar begins transmitting radar signals, such as chirps, e.g., sequentially, e.g., in accordance with a respective finite state machine of each millimeter-wave radar. In some embodiments, since each local timer is configured to expire at a different time, the (e.g., sequentially) transmitted chirps from each of the millimeter-wave radars occur at different times, thereby advantageously allowing for avoiding RF interference as well as for allowing for time-division multiplexing (TDM) of chirps from each millimeter-wave radar and for allowing operations such as beamforming, while using a single global trigger.

FIG. 2 shows waveforms 200 of signals of a millimeter-wave radar system, according to an embodiment of the present invention. The waveforms 200 of FIG. 2 correspond to an implementation of method 100 in accordance with an embodiment that uses an SPI Broadcast Mode, and that includes an application processor and first and second millimeter-wave radars.

Waveforms 200 illustrate an SPI clock signal SCLK, an SPI master out slave in (MOSI) signal MOSI, and SPI chip select (CS) signals CS₁ and CS₂ (corresponding to the first and second millimeter-wave radars).

As shown in FIG. 2 , a global trigger is sent (step 102) to both the first and second millimeter-wave radars simultaneously using an SPI write command. The global trigger is received by both the first and second millimeter-wave radars simultaneously at time t₁.

Upon receipt of the global trigger, an internal frame start signal is asserted (transitioned to an active state, in this case to a logic 1) to signal the beginning of the transmission process. As shown, each internal frame start signal FRAME_START₁ and FRAME_START₂ are asserted at the same time upon receipt of the global trigger. In some embodiments, there may be a delay between reception of the global trigger and when the internal frame start signals are asserted.

Each internal frame start signal (FRAME_START₁ and FRAME_START₂) starts a respective local counter (step 104) that counts until a predetermined count. Each respective count is unique so that each millimeter-wave radar exhibits a respective offset duration (t_(offset1) and t_(offset2)) from reception of the global trigger (from t₁) that is unique.

Upon elapsing of the respective offset duration (t_(offset1) and t_(offset2)), each millimeter-wave radar begins transmitting (step 106) a sequence of chirps (CHIRPS₁ and CHIRPS₂). As shown in FIG. 2 , the transmission of the first (CHIRPS₁) and second (CHIRPS₂) sequence of chirps (illustrated by assertion of signals CHIRPS₁ and CHIRPS₂, respectively) do not overlap.

FIG. 3 illustrates chirp transmissions and power amplifier states of the millimeter-wave radars of FIG. 2 , according to an embodiment of the present invention. The waveforms 300 of FIG. 3 correspond to an implementation of method loo, such as shown in FIG. 2 .

As shown in FIG. 3 , the sequence of chirps from the first and second millimeter-wave radars (CHIRPS₁ and CHIRPS₂, respective) do not overlap. As also shown in FIG. 3 , the active times of the respective power amplifies of the first and second millimeter-wave radars (PowerAmp₁ and PowerAmp₂) also do not overlap.

By avoiding overlap of chirps and active times of power amplifiers, some embodiments advantageously avoid RF interference between transmitted radar signals of the millimeter-wave radars. Some embodiments advantageously avoid RF interference without burdening the application processor to ensure correct timing.

Additional advantages of some embodiments include lower risk that the correct timing is not ensure due to, e.g., unexpected interrupts, that may consume processing resources, e.g., of the application processor.

FIGS. 2 and 3 illustrate an embodiment that includes two millimeter-wave radars and an application processor. It is understood that more than two millimeter-wave radars may be used such as n, where n is a positive integer greater than 2, such as 4, 5, 10, 16, 32, or more, and where the respective offset duration (t_(offset1), t_(offset2), . . . , t_(offsetn)) may be adjusted so that the there is no overlap between each respective sequence of chirps (CHIRPS₁, CHIRPS₂, . . . , CHIRPS_(n)).

FIG. 4 shows a flow chart of embodiment method 400 for programming and synchronizing multiple millimeter-wave radars, according to an embodiment of the present invention.

During step 402, the first millimeter-wave radar is programmed with a first time offset threshold, e.g., via a digital communication bus, such as via SPI. During step 404, the second millimeter-wave radar is programmed with a second time offset threshold, e.g., via a digital communication bus, such as via SPI.

In some embodiments, the programming of the first time offset threshold is performed, e.g., by the application processor via, e.g., SPI. In some embodiments, the programming of the first time offset threshold is performed, e.g., by an automated test equipment (ATE) during production testing of the millimeter-wave radars. Other implementations are also possible.

Steps 102, 104, and 106 may be performed, e.g., as described with respect to FIG. 1 .

FIG. 5 shows a schematic diagram of millimeter-wave system 500, according to an embodiment of the present invention. Millimeter-wave system 500 includes application processor 512, and millimeter-wave radars 514 and 518. Some embodiments may include more than two millimeter-wave radars, such as 3, 10, 64, or more.

During normal operation, application processor 512 configures the first and second time offset thresholds (steps 402 and 404) in respective registers 506 of millimeter-wave radars 514 and 518, where the first time offset threshold is different from the second time offset threshold. In some embodiments, application processor 512 may also configure other parameters (e.g., in other registers not shown in FIG. 5 ), such as distances between chirps, duration of chirps, chirp start and end frequencies, etc. Generally, however, the other parameters programmed may be the same for all millimeter-wave radars.

After configuring the first and second time offset thresholds, application processor 512 sends a global trigger (step 102) to millimeter-wave radars 514 and 518, e.g., using SPI bus 510. For example, in some embodiments, application processor 512 sends the global trigger using SPI Broadcast Mode. In other embodiments, the global trigger may be sent in other ways, such as by using a GPIO of application processor 512 that is coupled to both of the millimeter-wave radars 514 and 518.

When the global trigger is received, each millimeter-wave radar 514 and 518 starts their respective local timer 522. Each local timer is configured to generate a local trigger signal CHIRPS_TRIGGER when their respective time offset threshold is reached.

The local trigger signal then causes the respective controller 530 to begin transmitting chirps, e.g., sequentially (e.g., such as shown in FIGS. 3 and 4 ) using the respective millimeter-wave radar sensor circuit 536.

In some embodiments, since each local trigger CHIRPS_TRIGGER depends on the respective data programmed in respective register 506, it is possible to have controllers 530 with identical hardware for both millimeter-wave radars 514 and 518 while achieving non-overlapping chirp sequences when using a single global trigger, thereby advantageously relieving application processor 512 from the task of maintaining proper timing of the millimeter-wave radars 514 and 518.

Millimeter-wave radar system may be implemented, e.g., in a printed circuit board (PCB), where SPI bus 510 includes PCB traces coupling application processor 512 with millimeter-wave radars 514 and 518. In some embodiments, millimeter-wave radars 514 and 518 have identical hardware.

SPI master 502 and SPI slaves 504 may be implemented in any way known in the alt. For example, SPI slaves 504 may be implemented without support for SPI Broadcast Mode. In such embodiments, each millimeter-wave radar 514 and 518 may include a trigger terminal (not shown) coupled to a global trigger terminal of application processor 512 (not shown). In some embodiments, SPI slaves 504 may implement SPI Broadcast Mode.

Timer 522 may be implemented in any way known in the alt For example, in some embodiments, timer 522 may be implemented with a digital counter such as a digital up-counter that counts up, upon receipt of the frame start signal, to the time offset thresholds stored in register 506. Other embodiments may be implemented with a digital down-counter, or a digital up/down-counter, for example. Other implementations are also possible.

As shown in FIG. 5 , each of millimeter-wave radars 514 and 518 include SPI slave 504, controller 530, millimeter-wave radar sensor circuit 536, register 506, and timer 522. Each of millimeter-wave radars 514 and 518 is configured to perform radar functions, such as target detection and tracking, for example. Radar functions, such as target detection and tracking may be performed in any way known in the art.

In some embodiments, part or all of the radar operations may be performed in cooperation with application processor 512. For example, in some embodiments, millimeter-wave radars 514 and 518 may cooperate with application processor 512 to perform beamforming. Beamforming may be performed in any way known in the art. In some embodiments, millimeter-wave radars 514 and 518 may cooperate with application processor 512 to send the chirps in such a manner as to achieve time division multiplexing (TDM). For example, in some embodiments, raw data coming from different millimeter-wave radars (e.g., 514 and 518) can be used for TDM MIMO when the (e.g., known) delay is taken into account. Other radar functions are also possible.

Millimeter-wave radar sensor circuit 536 is configured to transmit and receive radar signals, such as chirps. In some embodiments, millimeter-wave radar sensor circuit 536 may be implemented as a frequency modulated continuous wave (FMCW) sensor.

Millimeter-wave radar sensor circuit 536 may be implemented in any way known in the att. For example, in some embodiments, millimeter-wave radar sensor circuit includes front-end RF circuit 538, and mixed signal circuit 546.

RF circuit 538 is configured to transmit signals (e.g., chirps) towards target(s) and to receive the echo (i.e., reflection) signal from the target(s) in its field of view using one or more antennas (not shown). RF circuit 538 includes transmitter circuit 540 and receiver circuit 542.

Transmitter circuit 540 and receiver circuit 542 may be implemented in any way known in the art. For example, in some embodiments, transmitter circuit 540 includes power amplifiers that amplify the chirps to be transmitted via one or more antenna(s) (not shown).

Mixed signal circuit 546 is configured to control RF circuit 538 to transmit signals (e.g., chirps), and to receive the echo signal. Mixed signal circuit 546 is also configured to translate the RF signals into digital signals that are then transmitted to controller 530.

Mixed signal circuit 546 may be implemented in any way known in the art. For example, in some embodiments, mixed signal circuit 546 includes one or more band-pass filters (BPFs), low-pass filters (LPFs), mixers, low-noise amplifier (LNA), intermediate frequency (IF) amplifiers, phase-locked loops (PLLs) and analog-to-digital converters (ADCs).

Controller 530 is configured to process the signals received from millimeter-wave radar sensor circuit 536 and transmit it to application processor 512, e.g., via SPI bus 510.

Controller 530 may be implemented in any way known in the aft, such as a general purpose controller or processor, application-specific integrated circuit (ASIC), or any other implementation. Controller 530 typically includes digital block 532 for general control purposes (e.g., controlling millimeter-wave radar sensor circuit 536) and a signal processing block 534 for processing the signals received from millimeter-wave radar sensor circuit 536. Digital block 532 may include a finite state machine (FSM), e.g., to control timing of the chirps transmitted. Signal processing block 534 may be implemented with a digital signal processor (DSP).

In some embodiments, millimeter-wave radar sensor circuit 536, controller 530, register 506, timer 522, and SPI slave 504 are implemented inside the same package. Some embodiments also include one or more antenna(s) (not shown) inside the same package. Other embodiments may implement one or more of the millimeter-wave radar sensor circuit 536, controller 530, register 506, timer 522, and SPI slave 504 as discrete components of the millimeter-wave radar, e.g., coupled to the same PCB. Other embodiments implement millimeter-wave system 500 using more than one PCB. Other implementations are also possible.

Application processor 512 may be implemented in any way known in the aft, such as a general purpose controller or processor, ASIC, or any other implementation.

FIG. 6 shows a schematic diagram of millimeter-wave system 600, according to an embodiment of the present invention. Millimeter-wave system 600 operates in a similar manner as millimeter-wave system 500. Millimeter-wave system 600, however, includes a global trigger line coupled between a GPIO of application processor 512 and the millimeter-wave radars 514 and 518. The global trigger line may be implemented, e.g., as a trace in the PCB.

Example embodiments of the present invention are summarized here. Other embodiments can also be understood from the entirety of the specification and the claims filed herein.

Example 1. A method including: receiving a global trigger with a first millimeter-wave radar; receiving the global trigger with a second millimeter-wave radar; generating a first internal trigger of the first millimeter-wave radar after a first offset duration from the global trigger; generating a second internal trigger of the second millimeter-wave radar after a second offset duration from the global trigger; start transmitting first millimeter-wave radar signals with the first millimeter-wave radar based on the first internal trigger; and start transmitting second millimeter-wave radar signals with the second millimeter-wave radar based on the second internal trigger, where the second offset duration is different from the first offset duration, and where the first and second millimeter-wave radar signals are transmitted sequentially so as to exhibit no temporal overlap.

Example 2. The method of example 1, further including generating the global trigger with an application processor.

Example 3. The method of one of examples 1 or 2, further including generating the global trigger using a general purpose input/output (GPIO) pin of the application processor, where the GPIO pin is coupled to the first and second millimeter-wave radars.

Example 4. The method of one of examples 1 to 3, further including generating the global trigger using a master out slave in (MOSI) line of a serial peripheral interface (SPI).

Example 5. The method of one of examples 1 to 4, further including: programming the first offset duration into the first millimeter-wave radar; and programming the second offset duration into the second millimeter-wave radar.

Example 6. The method of one of examples 1 to 5, further including: after receiving the global trigger by the first millimeter-wave radar, starting a first digital counter of the first millimeter-wave radar, and when a first count of the first digital counter reaches a first time offset threshold corresponding to the first offset duration, generating the first internal trigger; and after receiving the global trigger by the second millimeter-wave radar, starting a second digital counter of the second millimeter-wave radar, and when a second count of the second digital counter reaches a second time offset threshold corresponding to the second offset duration, generating the second internal trigger.

Example 7. The method of one of examples 1 to 6, where the first time offset threshold is stored in a first register of the first millimeter-wave radar, and where the second time offset threshold is stored in a second register of the second millimeter-wave radar.

Example 8. The method of one of examples 1 to 7, further including: programming the first time offset threshold into the first register; and programming the second time offset threshold into the second register.

Example 9. The method of one of examples 1 to 8, further including performing beamforming using the first and second millimeter-wave radars.

Example 10. A system including: an application processor configured to generate a global trigger; a first millimeter-wave radar including: a first timer configured to generate a first internal trigger after a first offset duration from the global trigger, a first millimeter-wave radar sensor circuit, and a first controller configured to generate first millimeter-wave radar signals based on the first internal trigger using the first millimeter-wave radar sensor circuit; and a second millimeter-wave radar that includes: a second timer configured to generate a second internal trigger after a second offset duration from the global trigger, a second millimeter-wave radar sensor circuit, and a second controller configured to generate second millimeter-wave radar signals based on the second internal trigger using the second millimeter-wave radar sensor circuit, where the second offset duration is different from the first offset duration so that the first and second millimeter-wave radar signals are transmitted sequential and without temporal overlap.

Example 11. The system of example 10, where the first millimeter-wave radar further includes a first serial peripheral interface (SPI) slave circuit, where the second millimeter-wave radar further includes a second SPI slave circuit, and where the application processor includes an SPI master circuit coupled to the first and second SPI slave circuits via an SPI bus.

Example 12. The system of one of examples 10 or 11, where the application processor is configured to send the global trigger to the first and second SPI slave circuits using the SPI bus.

Example 13. The system of one of examples 10 to 12, where the application processor is configured to: program the first offset duration into the first millimeter-wave radar using the SPI bus; and program the second offset duration into the second millimeter-wave radar using the SPI bus.

Example 14. The system of one of examples 10 to 13, further including a printed circuit board (PCB) coupled to the application processor, and to the first and second millimeter-wave radars, where the PCB includes the SPI bus.

Example 15. The system of one of examples 10 to 14, where the first timer includes a first counter, where the first millimeter-wave radar further includes a first register configured to store a first time offset threshold corresponding to the first offset duration, where the second timer includes a second counter, and where the second millimeter-wave radar further includes a second register configured to store a second time offset threshold corresponding to the second offset duration.

Example 16. The system of one of examples 10 to 15, where the first counter is configured to start counting up after receiving the global trigger, and to generate the first internal trigger when a first count of the first counter reaches the first time offset threshold, and where the second counter is configured to start counting up after receiving the global trigger, and to generate the second internal trigger when a second count of the second counter reaches the second time offset threshold.

Example 17. The system of one of examples 10 to 16, where the application processor is configured to send the global trigger using a GPIO terminal that is coupled to respective trigger terminals of the first and second millimeter-wave radars.

Example 18. A system including: an application processor configured to generate a global trigger; a first millimeter-wave radar including: a first trigger terminal configured to receive the global trigger, a first timer configured to generate a first internal trigger after a first offset duration from the global trigger, a first millimeter-wave radar sensor circuit, and a first controller configured to generate first millimeter-wave radar signals based on the first internal trigger using the first millimeter-wave radar sensor circuit; and a second millimeter-wave radar that includes: a second trigger terminal configured to receive the global trigger, a second timer configured to generate a second internal trigger after a second offset duration from the global trigger, a second millimeter-wave radar sensor circuit, and a second controller configured to generate second millimeter-wave radar signals based on the second internal trigger using the second millimeter-wave radar sensor circuit, where the second offset duration is different from the first offset duration so that the first and second millimeter-wave radar signals are transmitted sequentially and without temporal overlap.

Example 19. The system of example 18, where the first millimeter-wave radar further includes a first serial peripheral interface (SPI) slave circuit, where the second millimeter-wave radar further includes a second SPI slave circuit, where the application processor includes an SPI master circuit coupled to the first and second SPI slave circuits via an SPI bus, and where the application processor is configured to: program the first offset duration into the first millimeter-wave radar using the SPI bus; and program the second offset duration into the second millimeter-wave radar using the SPI bus.

Example 20. The system of one of examples 18 or 19, where the first timer includes a first counter, where the first millimeter-wave radar further includes a first register configured to store a first time offset threshold corresponding to the first offset duration, where the second timer includes a second counter, and where the second millimeter-wave radar further includes a second register configured to store a second time offset threshold corresponding to the second offset duration.

While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments. 

What is claimed is:
 1. A method comprising: transmitting a global trigger to first and second millimeter-wave radars via a serial bus using a data line of a first serial interface circuit without using a signal line dedicated only to the global trigger, wherein a frequency of the global trigger is less than a frequency of a clock signal of the first serial interface circuit; generating a first internal trigger of the first millimeter-wave radar in response to the global trigger; generating a second internal trigger of the second millimeter-wave radar in response to the global trigger; start transmitting first millimeter-wave radar signals with the first millimeter-wave radar based on the first internal trigger; and start transmitting second millimeter-wave radar signals with the second millimeter-wave radar based on the second internal trigger.
 2. The method of claim 1, further comprising generating the global trigger with an application processor.
 3. The method of claim 1, further comprising transmitting the global trigger via a master out slave in (MOSI) line of a serial peripheral interface (SPI).
 4. The method of claim 1, wherein: generating the first internal trigger comprises generating the first internal trigger of the first millimeter-wave radar after a first offset duration from the global trigger; and generating the second internal trigger comprises generating the second internal trigger of the second millimeter-wave radar after a second offset duration from the global trigger, wherein: the second offset duration is different from the first offset duration, and the first and second millimeter-wave radar signals are transmitted sequentially so as to exhibit no temporal overlap.
 5. The method of claim 4, further comprising: programming the first offset duration into the first millimeter-wave radar; and programming the second offset duration into the second millimeter-wave radar.
 6. The method of claim 4, further comprising: after receiving the global trigger by the first millimeter-wave radar, starting a first digital counter of the first millimeter-wave radar, and when a first count of the first digital counter reaches a first time offset threshold corresponding to the first offset duration, generating the first internal trigger; and after receiving the global trigger by the second millimeter-wave radar, starting a second digital counter of the second millimeter-wave radar, and when a second count of the second digital counter reaches a second time offset threshold corresponding to the second offset duration, generating the second internal trigger.
 7. The method of claim 6, wherein the first time offset threshold is stored in a first register of the first millimeter-wave radar, and wherein the second time offset threshold is stored in a second register of the second millimeter-wave radar.
 8. The method of claim 7, further comprising: programming the first time offset threshold into the first register; and programming the second time offset threshold into the second register.
 9. The method of claim 1, further comprising performing beamforming using the first and second millimeter-wave radars.
 10. A system comprising: an application processor comprising a first serial interface circuit coupled to a serial bus, the application processor configured to: generate a global trigger and transmit the global trigger to first and second millimeter-wave radars using a data line of the first serial interface circuit without using a signal line a dedicated only to the global trigger, wherein a frequency of the global trigger is less than a frequency of a clock signal of the first serial interface circuit; the first millimeter-wave radar comprising: a first local serial interface circuit coupled to the serial bus, the first local serial interface circuit configured to receive the global trigger via the serial bus, a first millimeter-wave radar sensor circuit, and a first controller configured to generate first millimeter-wave radar signals based on the first internal trigger using the first millimeter-wave radar sensor circuit; and the second millimeter-wave radar that comprises: a second local serial interface circuit coupled to the serial bus, the second local serial interface circuit configured to receive the global trigger via the serial bus, a second millimeter-wave radar sensor circuit, and a second controller configured to generate second millimeter-wave radar signals based on the second internal trigger using the second millimeter-wave radar sensor circuit.
 11. The system of claim 10, wherein the first local serial interface circuit comprises a first serial peripheral interface (SPI) slave circuit, wherein the second local serial interface circuit comprises a second SPI slave circuit, and wherein the first serial interface circuit comprises an SPI master circuit coupled to the first and second SPI slave circuits via an SPI bus.
 12. The system of claim 11, further comprising a printed circuit board (PCB) coupled to the application processor, and to the first and second millimeter-wave radars, wherein the PCB comprises the SPI bus.
 13. The system of claim 11, wherein: the first millimeter-wave radar further comprises a first timer configured to generate a first internal trigger after a first offset duration from the global trigger; the second millimeter-wave radar further comprises a second timer configured to generate a second internal trigger after a second offset duration from the global trigger; and the second offset duration is different from the first offset duration so that the first and second millimeter-wave radar signals are transmitted sequentially and without temporal overlap.
 14. The system of claim 13, wherein the application processor is configured to: program the first offset duration into the first millimeter-wave radar using the SPI bus; and program the second offset duration into the second millimeter-wave radar using the SPI bus.
 15. The system of claim 13, wherein the first timer comprises a first counter, wherein the first millimeter-wave radar further comprises a first register configured to store a first time offset threshold corresponding to the first offset duration, wherein the second timer comprises a second counter, and wherein the second millimeter-wave radar further comprises a second register configured to store a second time offset threshold corresponding to the second offset duration.
 16. The system of claim 15, wherein the first counter is configured to start counting up after receiving the global trigger, and to generate the first internal trigger when a first count of the first counter reaches the first time offset threshold, and wherein the second counter is configured to start counting up after receiving the global trigger, and to generate the second internal trigger when a second count of the second counter reaches the second time offset threshold.
 17. A system comprising: an application processor comprising a first serial interface circuit coupled to a serial bus, the application processor configured to: generate a global trigger and transmit the global trigger to first and second millimeter-wave radars using the first serial interface circuit without using a dedicated trigger line, wherein the global trigger is transmitted via a master out slave in (MOSI) of a serial peripheral interface (SPI); the first millimeter-wave radar comprising: a first local serial interface circuit coupled to the serial bus, the first local serial interface circuit configured to receive the global trigger via the serial bus, a first millimeter-wave radar sensor circuit, and a first controller configured to generate first millimeter-wave radar signals based on the first internal trigger using the first millimeter-wave radar sensor circuit; and the second millimeter-wave radar that comprises: a second local serial interface circuit coupled to the serial bus, the second local serial interface circuit configured to receive the global trigger via the serial bus, a second millimeter-wave radar sensor circuit, and a second controller configured to generate second millimeter-wave radar signals based on the second internal trigger using the second millimeter-wave radar sensor circuit.
 18. The system of claim 17, wherein: the first millimeter-wave radar further comprises a first timer configured to generate a first internal trigger after a first offset duration from the global trigger; the second millimeter-wave radar further comprises a second timer configured to generate a second internal trigger after a second offset duration from the global trigger; and the second offset duration is different from the first offset duration so that the first and second millimeter-wave radar signals are transmitted sequentially and without temporal overlap.
 19. The system of claim 18, wherein the first local serial interface circuit comprises a first SPI slave circuit, wherein the second local serial interface circuit comprises a second SPI slave circuit, wherein the first serial interface circuit comprises an SPI master circuit coupled to the first and second SPI slave circuits via an SPI bus, and wherein the application processor is configured to: program the first offset duration into the first millimeter-wave radar using the SPI bus; and program the second offset duration into the second millimeter-wave radar using the SPI bus.
 20. The system of claim 18, wherein the first timer comprises a first counter, wherein the first millimeter-wave radar further comprises a first register configured to store a first time offset threshold corresponding to the first offset duration, wherein the second timer comprises a second counter, and wherein the second millimeter-wave radar further comprises a second register configured to store a second time offset threshold corresponding to the second offset duration. 